The present invention relates to a processing apparatus having a ring member for holding a processing object such as a semiconductor wafer at an alignment position on a susceptor.
Generally in manufacturing a semiconductor integrated circuit, processing including film formation and pattern etching is repeatedly executed to form a large number of desired elements on a substrate such as a semiconductor wafer. Such processing is performed by placing the wafer on a susceptor inside a processing chamber, and then supplying processing gas such as film formation gas or etching gas from a shower head into the processing chamber while the interior of the processing chamber is kept in vacuum.
In this case, to ensure high processing uniformity in the plane of the wafer in, e.g., film formation and etching, the wafer must be aligned and placed on the susceptor with high precision and prevented from sliding and moving on the susceptor surface upon the placement. In particular, even a slight shift of the wafer within the plane or even a slight difference in horizontal level between the upper ends of lifter pins for vertically moving the wafer with respect to the susceptor may lead to sliding movement of the wafer on the susceptor upon placing the wafer on the support surface of the susceptor by the lifter pins.
In general, to prevent the movement of the wafer, an aligning guide ring having an inner diameter slightly larger than the diameter of the wafer is fixed to the peripheral edge portion of the susceptor, and the wafer is placed within the ring.
FIG. 10 is a schematic sectional view of a conventional susceptor. FIG. 11 is a plan view of the susceptor. As shown in FIGS. 10 and 11, a guide ring 4 having an L-shaped section is fitted on the peripheral edge portion of a thick disk-like susceptor 2. An inner diameter L1 of the guide ring 4 is set slightly larger than a diameter L2 of a wafer W by, e.g., about 1 mm. By placing the wafer W on the support surface of the susceptor 2 within the guide ring 4, the wafer W is aligned and prevented from largely moving, i.e., sliding on the support surface.
The susceptor 2 and the guide ring 4 are generally made of a ceramic material such as alumina (Al2O3) or aluminum nitride (AlN). If the constituent material of the susceptor 2 is the same as that of the guide ring 4, their thermal expansion coefficients are the same, and thus no problem occurs. If, however, their constituent materials are different, their thermal expansion coefficients are also different. The thermal expansion difference between the susceptor 2 and the guide ring 4 which are exposed to high temperatures up to, e.g., about 800xc2x0 C. exceeds an allowable value. As a result, the guide ring 4 may loosen or break.
As the wafer size increases to 8xe2x80x3 and 12xe2x80x3, the sizes of the susceptor 2 and the guide ring 4 also increases, and a slight difference in thermal expansion coefficient results in a large thermal expansion difference.
In recent years, in a plasma processing apparatus, it has been contemplated to use an alloy with high conductivity and excellent corrosion resistance for the susceptor itself in order to improve the uniformity of the plasma density by suppressing the potential difference within the support surface and the potential difference between the susceptor and the side wall of the chamber. In this case, however, the difference in thermal expansion coefficient between the alloy and the ceramic material forming the guide ring 4 becomes very large, and the guide ring may loosen or break, as described above.
In this case, the guide ring itself may be made of the same alloy material as that of the susceptor 2. However, since the thickness of the guide ring 4 is as small as, e.g., about 1 mm, if the guide ring 4 is made of an alloy material inferior in rigidity to the ceramic material, it thermally deforms and cannot stand practical use. Thus, such material is practically not employed.
The guide ring 4 is freely rotatable in the circumferential direction of the susceptor 2. For this reason, when, for example, the guide ring 4 is dismounted from the susceptor 2 for the purpose of maintenance, the guide ring 4 is very difficult to precisely mount back into its place.
It is an object of the present invention to provide a processing apparatus having an aligning ring member which neither breaks nor is misaligned even if the ring member is formed of a material with a thermal expansion coefficient different from that of a susceptor.
According to an aspect of the present invention, there is provided a processing apparatus comprising
a processing chamber,
a susceptor which is placed in the processing chamber and has one surface with a support area on which a processing object is set,
processing means for processing the processing object set on the support area,
an aligning ring member which is arranged on the surface of the susceptor so as to surround the support area, and defines movement of the processing object placed on the support area along the surface, and
movement regulating means, provided to the aligning ring member and the susceptor, for permitting relative movement of the aligning ring member and the susceptor in a radial direction due to thermal expansion/contraction difference of the alignment ring member and the susceptor while prohibiting relative rotation thereof.
In this processing apparatus, even if the temperatures of the susceptor and the ring member change upon repeat processing for processing objects, and a thermal expansion difference is generated between the susceptor and the ring member, the expansion/contraction amount is absorbed by the movement regulating means. Therefore, the aligning ring member can be prevented from receiving excessive stress and breaking, and in addition from loosening.
Further, the aligning ring member itself can be aligned with the susceptor.